Fix overloading for IDBDatabase transaction

Fix overloading for IDBDatabase transaction

Use the underlying dart implementation class in overloading resolution
checks, rather than the dart interface which is presented to the
user.  This resolves an issue with IDBDatabase in which DOMStringList
and sequence<DOMString> have the same Dart interface type
(List<String>), even though the underlying implementation types differ
(List<String> vs DomStringList).

BUG=
R=vsm@google.com

Committed: https://code.google.com/p/dart/source/detail?r=37883

[vsm, 2014-07-01 04:53:59]

lgtm

[Leaf, 2014-07-01 17:24:52]

Committed patchset #1 manually as r37883 (presubmit successful).